The steel County class cruiser HMS Sussex was launched from the Hebburn yard of R and W Hawthorn, Leslie and Co Ltd, Heyburn (Yard No 544) on 22nd February 1928. She measured 633.0′ x 66.0′ x 21.0′ and her tonnage was 9750 displacement tons. She was powered by eight Admiralty 3-drum boilers and 4 x four shaft Parsons geared turbines delivering 80,000 shaft horse power. She was armed with 8 x 8 inch dual guns, 4 x 4 inch single anti-aircraft guns, 4 x 2 pounder single pom-pom guns, 2 x 2 pounder quad pom-pom guns, 2 x 0.5 inch quadruple Vickers machine guns, 2 x quadruple 21 inch torpedo tubes.
After her launch and commissioning Sussex served in the Mediterranean until 1934, when she was sent to serve on an exchange tour with the Royal Australian Navy while HMAS Australia operated with the Mediterranean Fleet. In 1936 she resumed her presence in the Mediterranean until 1939 including duty defending neutral shipping along the eastern Spanish coast during the last days of the Spanish Civil War. After the outbreak of war in 1939 she operated with Force H in the South Atlantic during the search for the enemy German raider Admiral Graf Spee. Following the scuttling of the Graf Spee in December 1939, she returned to the UK and served with the Home Fleet during the Norwegian Campaign.
She was sent to Glasgow for a refit in September 1940, and while undergoing work, was struck by bombs on 18th September. These caused serious fires, gutting the after end, and she settled on the bottom with a heavy list. She needed extensive repairs and did not return to service until August 1942.